全文获取类型
收费全文 | 1603篇 |
免费 | 140篇 |
国内免费 | 2篇 |
专业分类
1745篇 |
出版年
2022年 | 14篇 |
2021年 | 35篇 |
2020年 | 15篇 |
2019年 | 22篇 |
2018年 | 31篇 |
2017年 | 28篇 |
2016年 | 40篇 |
2015年 | 69篇 |
2014年 | 79篇 |
2013年 | 98篇 |
2012年 | 121篇 |
2011年 | 111篇 |
2010年 | 69篇 |
2009年 | 62篇 |
2008年 | 86篇 |
2007年 | 90篇 |
2006年 | 80篇 |
2005年 | 70篇 |
2004年 | 73篇 |
2003年 | 72篇 |
2002年 | 71篇 |
2001年 | 11篇 |
2000年 | 15篇 |
1999年 | 17篇 |
1998年 | 23篇 |
1997年 | 12篇 |
1996年 | 11篇 |
1995年 | 14篇 |
1994年 | 8篇 |
1993年 | 16篇 |
1992年 | 14篇 |
1991年 | 10篇 |
1990年 | 11篇 |
1989年 | 7篇 |
1988年 | 8篇 |
1987年 | 9篇 |
1986年 | 8篇 |
1985年 | 11篇 |
1984年 | 14篇 |
1983年 | 18篇 |
1982年 | 13篇 |
1981年 | 10篇 |
1980年 | 17篇 |
1978年 | 7篇 |
1977年 | 10篇 |
1976年 | 10篇 |
1974年 | 7篇 |
1968年 | 5篇 |
1964年 | 6篇 |
1960年 | 5篇 |
排序方式: 共有1745条查询结果,搜索用时 15 毫秒
101.
Biglycan is a Class I Small Leucine Rich Proteoglycans (SLRP) that is localized on human chromosome Xq28-ter. The conserved nature of its intron-exon structure and protein coding sequence compared to decorin (another Class I SLRP) indicates the two genes may have arisen from gene duplication. Biglycan contains two chondroitin sulfate glycosaminoglycan (GAG) chains attached near its NH2 terminus making it different from decorin that has only one GAG chain. To determine the functions of biglycan in vivo, transgenic mice were developed that were deficient in the production of the protein (knockout). These mice acquire diminished bone mass progressively with age. Double tetracycline-calcein labeling revealed that the biglycan deficient mice are defective in their capacity to form bone. Based on this observation, we tested the hypothesis that the osteoporosis-like phenotype is due to defects in cells critical to the process of bone formation. Our data shows that biglycan deficient mice have diminished capacity to produce marrow stromal cells, the bone cell precursors, and that this deficiency increases with age. The cells also have reduced response to tranforming growth factor- (TGF-), reduced collagen synthesis and relatively more apoptosis than cells from normal littermates. In addition, calvaria cells isolated from biglycan deficient mice have reduced expression of late differentiation markers such as bone sialoprotein and osteocalcin and diminished ability to accumulate calcium judged by alizerin red staining. We propose that any one of these defects in osteogenic cells alone, or in combination, could contribute to the osteoporosis observed in the biglycan knockout mice. Other data suggests there is a functional relationship between biglycan and bone morphogenic protein-2/4 (BMP 2/4) action in controlling skeletal cell differentiation. In order to test the hypothesis that functional compensation can occur between SLRPs, we created mice deficient in biglycan and decorin. Decorin deficient mice have normal bone mass while the double biglycan/decorin knockout mice have more severe osteopenia than the single biglycan indicating redundancy in SLRP function in bone tissue. To further determine whether compensation could occur between different classes of SLRPs, mice were generated that are deficient in both biglycan (class I) and fibromodulin, a class II SLRP highly expressed in mineralizing tissue. These doubly deficient mice had an impaired gait, ectopic calcification of tendons and premature osteoarthritis. Transmission electron microscopy analysis showed that like the decorin and biglycan knockouts, they have severely disturbed collagen fibril structures. Biomechanical analysis of the affected tendons showed they were weaker compared to control animals leading to the conclusion that instability of the joints could be the primary cause of all the skeletal defects observed in the fibromodulin/biglycan knockout mice. These studies present important new animal models for musculoskeletal diseases and provide the opportunity to characterize the network of signals that control tissue integrity and function through SLRP activity. Published in 2003. 相似文献
102.
The C-terminal region of Escherichia coli UvrC contributes to the flexibility of the UvrABC nucleotide excision repair system
下载免费PDF全文
![点击此处可从《Nucleic acids research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Verhoeven EE van Kesteren M Turner JJ van der Marel GA van Boom JH Moolenaar GF Goosen N 《Nucleic acids research》2002,30(11):2492-2500
Nucleotide excision repair in Escherichia coli involves formation of the UvrB–DNA complex and subsequent DNA incisions on either site of the damage by UvrC. In this paper, we studied the incision of substrates with different damages in varying sequence contexts. We show that there is not always a correlation between the incision efficiency and the stability of the UvrB–DNA complex. Both stable and unstable UvrB–DNA complexes can be efficiently incised. However some lesions that give rise to stable UvrB–DNA complexes do result in a very low incision. We present evidence that this poor incision is due to sterical hindrance of the damage itself. In its C-terminal region UvrC contains two helix–hairpin–helix (HhH) motifs. Mutational analysis shows that these motifs constitute one functional unit, probably folded as one structural unit; the (HhH)2 domain. This (HhH)2 domain was previously shown to be important for the 5′ incision on a substrate containing a (cis-Pt)·GG adduct, but not for 3′ incision. Here we show that, mainly depending on the sequence context of the lesion, the (HhH)2 domain can be important for 3′ and/or 5′ incision. We propose that the (HhH)2 domain stabilises specific DNA structures required for the two incisions, thereby contributing to the flexibility of the UvrABC repair system. 相似文献
103.
Natural substrate/product binding activates medium-chain acyl-CoA dehydrogenase (MCAD) to accept electrons from its substrate by inducing a positive flavin midpoint potential shift. The energy source for this activation has never been fully elucidated. If ground-state alterations of the ligand, such as polarization, are entirely responsible for enzyme activation, the ligand potential should shift equally to that of the flavin but in the opposite direction. Ligand polarization is likely responsible for only a small portion of this activation. Here, thiophenepropionoyl- and furylpropionoyl-CoA analogs were used to directly measure the redox modulations of several ligand couples upon binding to MCAD. These measurements identified the thermodynamic contribution of ligand polarization to enzyme activation. Because the ligand potential alterations are significantly smaller than modulations in the flavin potential due to binding, other phenomena such as pK(a) changes, desolvation, and charge alterations are likely responsible for the thermodynamic modulations required for MCAD's activity. 相似文献
104.
Woo AL Gildea LA Tack LM Miller ML Spicer Z Millhorn DE Finkelman FD Hassett DJ Shull GE 《The Journal of biological chemistry》2002,277(50):49036-49046
Mice lacking NHE3, the major absorptive Na(+)/H(+) exchanger in the intestine, are the only animal model of congenital diarrhea. To identify molecular changes underlying compensatory mechanisms activated in chronic diarrheas, cDNA microarrays and Northern blot analyses were used to compare global mRNA expression patterns in small intestine of NHE3-deficient and wild-type mice. Among the genes identified were members of the RegIII family of growth factors, which may contribute to the increased absorptive area, and a large number of interferon-gamma-responsive genes. The latter finding is of particular interest, since interferon-gamma has been shown to regulate ion transporter activities in intestinal epithelial cells. Serum interferon-gamma was elevated 5-fold in NHE3-deficient mice; however, there was no evidence of inflammation, and unlike conditions such as inflammatory bowel disease, levels of other cytokines were unchanged. In addition, quantitative PCR analysis showed that up-regulation of interferon-gamma mRNA was localized to the small intestine and did not occur in the colon, spleen, or kidney. These in vivo data suggest that elevated interferon-gamma, produced by gut-associated lymphoid tissue in the small intestine, is part of a homeostatic mechanism that is activated in response to the intestinal absorptive defect in order to regulate the fluidity of the intestinal tract. 相似文献
105.
Kuczek M 《Cellular & molecular biology letters》2003,8(1):85-95
The nonallosteric regulation mechanism of enzyme reaction velocity assumes that the substrate and enzyme interact via a metal cation and form simple and mixed, mono- and multi-nuclear complexes. A solution of equations for individual cases gives a function of initial reaction velocity at any given substrate or modifier concentration. This function can describe kinetic effects that are considered allosteric, as well as phenomena omitted by commonly-accepted models. 相似文献
106.
107.
Meek IB Peplow AW Ake C Phillips TD Beremand MN 《Applied and environmental microbiology》2003,69(3):1607-1613
Many Fusarium species produce one or more agriculturally important trichothecene mycotoxins, and the relative level of toxicity of these compounds is determined by the pattern of oxygenations and acetylations or esterifications on the core trichothecene structure. Previous studies with UV-induced Fusarium sporotrichioides NRRL 3299 trichothecene mutants defined the Tri1 gene and demonstrated that it was required for addition of the oxygen at the C-8 position during trichothecene biosynthesis. We have cloned and characterized the Tri1 gene from NRRL 3299 and found that it encodes a cytochrome P450 monooxygenase. The disruption of Tri1 blocks production of C-8-oxygenated trichothecenes and leads to the accumulation of 4,15-diacetoxyscirpenol, the same phenotype observed in the tri1 UV-induced mutants MB1716 and MB1370. The Tri1 disruptants and the tri1 UV-induced mutants do not complement one another when coinoculated, and the Tri1 gene sequence restores T-2 toxin production in both MB1716 and MB1370. The DNA sequence flanking Tri1 contains another new Tri gene. Thus, Tri1 encodes a C-8 hydroxylase and is located either in a new distal portion of the trichothecene gene cluster or in a second separate trichothecene gene cluster. 相似文献
108.
Kovarova H Hajduch M Livingstone M Dzubak P Lefkovits I 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2003,787(1):53-61
In this paper we focus on the detection of specific state of protein phosphorylation within a complex protein mixture separated by two-dimensional gel electrophoresis followed by immunoblotting. The availability of antibodies that specifically recognize the phosphorylated residue(s) of proteins make this approach feasible as exemplified by the study of the regulatory mechanisms of the cell cycle. The major advantage of the presented approach is its relative simplicity and sensitivity that allows specific detection of protein phosphorylation and distinguishes different phosphorylation sites of target protein. Current findings demonstrate that this method represents a reasonable alternative to the use of other tools to study protein phosphorylation. 相似文献
109.
Grzelak K Kłdkiewicz B Kolomiets LI Debski J Dadlez M Lalik A Ozyhar A Kochman M 《Protein expression and purification》2003,31(2):173-180
Galleria mellonella juvenile hormone binding protein (JHBP) is a single chain glycoprotein with two disulfide bonds and a molecular mass of 25,880 Da. This report describes the expression of JHBP in bacteria and yeast cells (Pichia pastoris). The expression in bacteria was low and the protein was rapidly degraded upon cell lysis. The expression of His8-tagged rJHBP (His8-rJHBP) in P. pastoris was high and the non-degraded protein was purified to homogeneity with high yield in a one-step immobilized Ni++ affinity chromatography. His8-rJHBP from P. pastoris contains one JH III binding site with KD of 3.7 +/- 1.3x10(-7) M. The results suggest that P. pastoris is the preferred system for expression of His8-rJHBP in non-degraded fully active form. 相似文献
110.
The TAK1-NLK mitogen-activated protein kinase cascade functions in the Wnt-5a/Ca(2+) pathway to antagonize Wnt/beta-catenin signaling 总被引:4,自引:0,他引:4